This invention relates to friction clutches and transmissions for large automotive vehicles.
A clutch brake has generally a flat and annular shape, and is splined onto the transmission input shaft in between the release bearing mechanism and the transmission. Upon disengagement of the main clutch of the vehicle, the clutch brake retards and stops the rotation of the driven shaft so that a smooth gear shifting operation may be performed. Because of its relatively small size and torsional forces to which it is subjected during use, replacement of the clutch brake is often required prior to the replacement of the main clutch transmission.
A number of clutch brake designs are in use, and each of the known designs has some disadvantages, mostly related to the assembly, installation and/or removal of the clutch brake. These known designs may be categorized according to their installation procedure, and are available in three versions: (1) a unitary annular assembly, (2) an assembly with two separate mating halves, and (3) a hinged assembly.
The unitary assembly, although inexpensive, is replaced by partially disassembling the clutch, lowering the transmission, or by fracturing the clutch brake in two places to allow its removal. All three replacement options are costly, the last one also being potentially dangerous.
Clutch brakes that comprise mating halves assembled and secured to form an annular assembly are exemplified by the clutch brakes shown in U.S. Pat. No. 4,512,450 to Babcock, U.S. Pat. No. 5,031,739 to Flotow et al., U.S. Pat. No. 5,076,406 to Gregory et al., and U.S. Pat. No. 5,435,425 to Ijames. These clutch brakes have their two halves connected through various methods and fasteners.
The subsequent evolution of the clutch brake resulted in hinged-type brakes, which have been well received by the market. Such brakes are shown in U.S. Pat. No. 5,285,881 to Lero et al., U.S. Pat. No. 6,450,310 to Catrinta (the inventor of the clutch brake disclosed herein), and in U.S. Pat. No. 7,311,183 to Black, Jr. et al. These patents disclose clutch brakes comprised of two arcuate members pivotally connected to each other at one end and connected by other means at the second end to form a closed annular assembly about the shaft. The hinged-type clutch brakes offer an easier installation and removal as compared with the two-piece clutch brakes.
Some clutch brakes include a torque-limiting feature. Torque-limiting designs reduce the frequency of replacement necessary by improving the clutch brake longevity and provide a higher safety factor for the transmission and the clutch. This is accomplished by permitting the clutch brake to slip when excessive braking pressure is applied to the brake, thereby avoiding the excessive stress which contributes to wear and tear. A number of patents (U.S. Pat. No. 3,763,977 to Sink, U.S. Pat. No. 4,043,437 to Taylor, U.S. Pat. No. 4,046,237 to Taylor, U.S. Pat. No. 4,186,826 to MacKendrick et al., U.S. Pat. No. 4,657,124 to Flotow, U.S. Pat. No. 4,762,215 to Flotow et al., U.S. Pat. No. 4,782,926 to Kitano et al., and U.S. Pat. No. 4,807,730 to Kitano et al., and U.S. Pat. No. 4,947,969 to Tarlton) teach the use of a particular friction coupling between an outer housing and inner collar member. When the torsional force between the housing and collar is too great, they slip relative to each other and thereby avoid damage. Also, unlike traditional designs, a torque-limiting clutch brake will not disrupt vehicle operation when improperly applied.
While torque-limiting designs work relatively well for their intended purpose, the clutch brake will still eventually fail and must be replaced. Thus, for known torque-limiting clutch brake designs, the clutch brake must be replaced by lowering and disassembling the clutch and transmission.
The splittable sections concept to facilitate installation and replacement was first addressed relative to torque-limiting clutch brakes in U.S. Pat. No. 5,099,970 to Harris, followed by U.S. Pat. No. 5,415,256 to Weigand et al. Harris discloses a splittable torque-limiting clutch brake which utilizes a detent mechanism as the torque limiting feature, instead of a friction type mechanism. Use of the detent mechanism facilitates making the device in splitable halves which can be installed without removing the clutch and transmission from the vehicle. Weigand et al. provide a multi-piece friction type torque-limiting clutch brake which is also splittable into halves for easy removal and installation.
Although the concept disclosed in these two patents combines the ease of replacement with the torque-limiting feature, there are drawbacks to the designs. Specifically, the relative complexity and fragility of most of the components of these clutch brakes render them unsuitable for the harsh environment in which they must operate.
Accordingly, it is an object of the present invention to provide a torque-limiting clutch brake assembly that is easily installed on and removed from the transmission input shaft without damage to the clutch brake.
It is a further object of the present invention to provide a torque-limiting clutch brake that may be installed or removed without use of special tools and, more specifically, may be installed or removed manually.